1. Field of the Invention
The present invention relates to a micro-actuator used as a device for a micro-electro-mechanical system (MEMS) and, more particularly, to a method for fabricating a micro-structure and micro-actuator, which can simply and easily fabricate the micro-structure and micro-actuator using an aligned nano-material array adhesive.
2. Description of the Related Art
In general, a micro-electro-mechanical system (MEMS) refers to a technology that combines an apparatus, in which sensor, valves, gears, reflectors, actuators, electronic circuits, etc., are integrated on a single silicon substrate, or a microscale mechanism, which is mounted in a semiconductor chip, with a computer.
The MEMS technology has evolved from a silicon fabrication process that produces semiconductor chips and, in order to fabricate miniature mechanical components such as valves, motors, pumps, gears, etc. with a three-dimensional structure on a silicon substrate, various MEMS technologies such as surface micromachining, bulk micromachining involving deep etching, lithographie-galvanoformung-abformung (LIGA), etc. have been developed.
Meanwhile, an electrostatically-actuated micro-scanner manufactured based on the MEMS technology is a device that scans optical signals by rotating a micro-mirror using a micro-actuator to change the direction of light. This micro-scanner has various advantages such as low power consumption, high operating speed, low fabrication cost, etc. and thus is applied to various industries and consumer electronics, and its application is expected to gradually expand.
The micro-actuator installed in the micro-scanner refers to a microscale device configured to be driven by an attractive force produced due to collection of charges caused when a voltage difference occurs between two electrodes which are spaced a predetermined distance from each other. The micro-actuator may be broadly classified into a parallel plate actuator and a comb-drive actuator depending on the structure of a stator electrode and a rotor electrode.
The parallel plate actuator operates a micro-mirror using the attractive force between two plates to which a voltage is applied and is generally operated by applying a potential difference between the mirror and a substrate located at a predetermined distance from the bottom of the mirror. The comb-drive actuator has a structure in which comb-shaped rotor electrode and stator electrode are staggered alternately and is configured to move the rotor toward the stator using the attractive force produced when a potential difference is applied between the two electrodes.
The comb-drive actuator may be classified into an in-plane comb-drive actuator and a vertical comb-drive actuator of staggered vertical comb-drive (SVC) type and angular vertical comb-drive (AVC) type. The in-plane comb-drive actuator has a structure in which a rotor electrode and a stator electrode are installed on a plane such that the rotor electrode moved toward the stator, thus causing linear motion in the plane.
The vertical capacitive micro-actuator of staggered vertical comb-drive (SVC) type is fabricated to have a predetermined height difference in a state where a stator electrode and a rotor electrode are engaged with each other such that when a potential difference is applied between the two electrode, the rotor receives the attractive force in the direction of the stator and is restrained by a torsion bar, thus using rotary motion with respect to the torsion bar.
The vertical capacitive micro-actuator of angular vertical comb-drive (AVC) type has a structure in which a rotor electrode has an initial rotational angle with respect to a torsion bar and, when an operating voltage is applied between the two electrodes, the rotor electrode is drawn in the direction of the stator electrode and rotated until the stator electrode and the rotor electrode completely overlap each other.
When the vertical capacitive micro-actuator of angular vertical comb-drive (AVC) type is fabricated, the rotor electrode and the stator electrode are engaged with each other in the same plane by a simple micro-processing process and then the rotor electrode has a predetermined initial rotational angle by a post process.
Next, prior art methods to fabricate the vertical capacitive micro-actuators will be described in brief.
First, in the paper of “J. Kim, D. Christensen, and L. W. Lin, entitled: Micro vertical comb actuators by selective stiction process, Sensors and Actuators A-Physical, vol. 127, pp. 248-254, Mar. 13 2006” a selective stiction process is employed to fabricate a vertical comb-drive actuator.
This paper discloses a method for fabricating a vertical comb-drive actuator by causing the selective stiction when an oxide silicon layer located at the bottom of a device silicon layer of a silicon-on-insulator (SOI) wafer is etched to provide an initial vertical height difference between a rotor and a stator.
Moreover, in the paper of “D. Lee, U. Krishnamoorthy, K. Yu, and O. Solgaard, entitled: Single-crystalline silicon micromirrors actuated by self-aligned vertical electrostatic combdrives with piston-motion and rotation capability, Sensors and Actuators A-Physical, vol. 114, pp. 423-428, 2004”, another method for fabricating a vertical comb-drive actuator is disclosed.
According to this paper, a vertical comb-drive actuator is fabricated to have a structure in which structures corresponding to a stator and a rotor are formed on an upper silicon layer and a lower silicon layer, respectively, which are electrically insulated from each other by additionally bonding a silicon water to an SOI wafer and then selectively etching a plurality of silicon layers and insulating layers.
Furthermore, in the paper of “J. Kim, H. Choo, L. W. Lin, and R. S. Muller, entitled: Microfabricated torsional actuators using self-aligned plastic deformation of silicon, Journal of Microelectromechanical Systems, vol. 15, pp. 553-562, June 2006”, still another method for fabricating a vertical comb-drive actuator is disclosed.
According to this study, a vertical comb-drive actuator is fabricated in such a manner that a comb structure is formed by a micro-processing process, a stress is applied to a silicon torsion bar using a jig structure additionally fabricated, and the silicon torsion bar is heated to be permanently deformed, thus causing an initial vertical position difference between a stator and a rotor.
As mentioned above, the existing vertical capacitive micro-actuator is subjected to an additional process such as etching to cause the selective stiction, selective etching of the plurality of silicon layers and insulating layers after additionally bonding the silicon wafer, or heat treatment to permanently deform the silicon torsion bar, in addition to the micro-processing process.
As such, while the conventional vertical capacitive micro-actuators are widely applied to various fields such as optical communications, biomedical engineering, image scanning devices, etc., complicated fabrication processes are required, which reduces the fabrication yield, thus making it difficult to reduce the fabrication cost. In particular, among the vertical capacitive actuators, the micro-actuator of AVG type, which is known as having excellent performance, has drawbacks in that the micro-processing process to fabricate the device is complicated, which makes it more difficult to increase the fabrication yield, acting as an obstacle to commercialization.